Tuesday, February 23, 2010

The International Research Institute (IRI) for Climate and Society at Columbia University is the latest forecasting agency to affirm enhanced probability for a largely ‘normal' monsoon for India this year.

But the initial phase leading up to the onset phase and advancement (April-May-June) is loaded with probability for below normal precipitation for eastern India – covering north coastal Andhra Pradesh, Vidarbha, Orissa, Chhattisgarh, Jharkhand, Bihar and Gangetic West Bengal.

BEYOND BORDER

While north-east India could likely see normal onset and advancement conditions, probability for below normal precipitation is indicated for neighbouring countries of Bangladesh, Myanmar, Thailand, Vietnam, Laos, and parts of south and west China.

Northern half of Pakistan is tipped to receive excess showers during this phase, while ‘drought masking' is applicable for the southern half, the IRI outlook suggested.

May-June-July that coincides with advancement and maturity of the monsoon is projected to return normal rainfall figures for entire India (including east India that may have gone under-fed until then) and Pakistan.

But the enhanced probability for below-normal precipitation would be still valid for Bangladesh-Myanmar, Vietnam and Thailand.

The fully mature monsoon during June-July-August is once again shown to be normal over India, Pakistan, entire South-East Asia and China.

This is the phase that scientists at the Tokyo-based Research Institute for Global Change (RIGC) have identified with the dying of the prevailing El Nino conditions over central Pacific and likely return of the reverse phenomenon of La Nina.

A La Nina has been traditionally considered to favour a concurrent Indian monsoon, though not with direct cause-effect relationship.

The RIGC has said in updated forecast that it expects to see a weak positive Indian Ocean Dipole at work during September-October-November.

PENINSULAR HEATING

Like La Nina, a positive IOD is also known to rub off positively on the Indian monsoon, though the timing would be too late for this year.

In positive IOD conditions, warm temperature anomalies shift to western Indian Ocean, helping catalyse the favourable impact on monsoon for mainland India, especially the central and western parts.

As for expected temperature regime for the country, the IRI said that the odds have stacked up to signal enhanced probability for some of the worst heating to get concentrated over peninsular India during March-April-May and April-May-June.

This region would have to wait until after the monsoon has entrenched its presence in May-June-July to get some reprieve, the IRI forecasts indicate. There is up to 70 per cent probability that this region, along with most of the west coast, would be subjected to maximum heating (to a level variously higher than even in the northwest) during the two back-to-back quarters.

Meanwhile, India Meteorological Department (IMD) has gone on record saying that the threat from El Nino, which contributed to the worst monsoon rains in India in nearly four decades last year, has subsided, raising hopes of ‘normal' monsoon rains this year.

WESTERN DISTURBANCES

On Sunday, the IMD said that it expected back-to-back western disturbances to drift into the northwest during this week from across the border signalling snow and rains for the hilly regions and adjoining respectively.

The first in the series is forecast to affect northwest India on Monday and Tuesday while the follow-up system is tipped to enter the region from Thursday even as northwesterly to westerly winds have gathered pace over the plains. Minimum temperatures are expected to look up during the arrival phase of the systems.

An IMD outlook for the next few days said that isolated rain or snow would occur over Jammu and Kashmir on Sunday while it would be and scattered on the next two days. Isolated to scattered rain and snow has been indicated for Himachal Pradesh and Uttarakhand as well on Monday and Tuesday. Isolated rain or thundershowers might occur over plains of northwest India.